TTYs (also known as TDDs) are text terminals that people with speaking and hearing impairments use in order to communicate over telephone lines. In the United States, the most commonly used TTY communication protocol is the technique specified by ANSI/TIA/EIA 825 (“A 45.45 Baud FSK Modem”). Relevant characteristics of this protocol include the following:
(1) TTYs are silent when not transmitting. Unlike fax machines and computer modems, TTYs have no “handshake” procedure at the start of a call, nor do they have a carrier tone during the call. Although this approach tends to limit the speed of transmission, it has the advantage of permitting TTY tones, DTMF (Dual Tone Multi-Frequency signals, also known as “touch tones”), and voice to be intermixed on the same call.
(2) Operation is “half duplex.” TTY users must take turns transmitting, and typically cannot interrupt each other. If both people try to type at the same time, their TTYs will show no text at all, or will show text that is gibberish. There is no automatic mechanism that lets TTY users know when a character they have typed correctly has been received incorrectly. To avoid this problem, a user normally types a message and then types “GA” (for go ahead). This does solve the problem of half duplex operation but results in a slow, jerky operation which tends to limit spontaneous interaction.
(3) Each TTY character consists of a sequence of seven individual tones. The first tone is always a “start tone” at 1800 Hz. This is followed by a series of five tones, at either 1400 or 1800 Hz, which specify the character. The final tone in the sequence is always a “stop tone” at 1400 Hz. The “stop tone” is a border that separates this character from the next. Each of the first six tones is 22 milliseconds in duration. The final “stop tone” is usually 33 milliseconds, but is permitted to be as long as 44 milliseconds. This means that the duration of each TTY character is at least 165 milliseconds, which works out to approximately six characters per second. (The description of this as a “45.45 Baud” protocol is based on the number of 22-millisecond tones that can be transmitted in one second, not the number of characters.)
From a usability perspective, one of the benefits to using a half-duplex, carrier-free protocol for TTYs is that it is possible to intermix voice and TTY transmissions on the same call. This is important because some people who use TTYs are individuals with speech loss who nevertheless are able to hear; these individuals often prefer to transmit with their TTYs and then hear the response, a process commonly referred to as Hearing Carry Over or HCO. Individuals with hearing loss, but who are nevertheless able to speak clearly, often prefer to receive with their TTYs and then speak in response; this is commonly referred to as Voice Carry Over or VCO.
From a usability perspective, this protocol also has several disadvantages, including: (1) TTY users must take turns typing to each other, and are unable to interrupt each other. (2) HCO and VCO users need a TTY device or specialized telephone in order to communicate. (3) People who receive a TTY message in their voicemail mailbox (which may include mailbox owners who have no communication disabilities, and therefore no easy access to a TTY device), need a TTY device or specialized software to read the message. (4) The absence of handshake tones means that there is no automatic mechanism by which to detect that a person is a TTY user until that person starts typing. (5) The protocol itself, although very robust when used in conjunction with traditional circuit-switched analog or digital telephony systems, tends to be unreliable when used in telephony systems that employ packet switching (e.g., Voice over Internet Protocol networks) or voice-optimized audio compression techniques (e.g., the GSM encoding used in many wireless systems).
The 45.45 Baud FSK protocol has been used in United States TTYs since 1963, and is based largely on the protocol that was used in military teletypewriters during the Second World War. Quite obviously, modern techniques would permit the development of new protocols that retain the advantages of the current protocol, while eliminating the disadvantages. Although many new protocols with excellent capabilities have been proposed, an important barrier stands in the way of their general acceptance: by some estimates, as many as 4,000,000 TTYs that use the 45.45 Baud protocol have been manufactured and distributed since 1963. This constitutes an enormous embedded base that cannot be upgraded or replaced economically. For this reason, it is desirable to solve the usability problems in a manner that does not require the 45.45 Baud protocol, and millions of current-generation TTY devices, to be abandoned.
Among the above-listed problems associated with the 45.45 Baud protocol, the issue that has been addressed explicitly in recent prior art concerns the inability of packet switched networks or voice-optimized compression codecs to support reliable TTY communication. Attention has been paid to these problems largely because, in the United States, Section 508 of the Workforce Investment Act of 1998, as well as Sections 251(a)(2) and 255 of the Telecommunication Act of 1996, require telephony systems to be TTY compatible.
With regard specifically to an issue addressed by this submission, FIGS. 1 and 2 illustrate the problems of performing HCO operations with a standard, 45.45 Baud, TTY such as TTY 102. To transmit or receive TTY information to other party 109, user 108 has to place the handset 107 into TTY 102 as illustrated in FIG. 1. FIG. 3 illustrates a pictorial view of a telephone and TTY such as shown in FIG. 1 having telephone 301 and TTY 302. If user 108 wants to use HCO operations, user 108 has to transmit TTY information as illustrated in FIG. 1, but hears by first removing handset 107 from the acoustic coupler of TTY 102 as illustrated in FIG. 2 and then hearing. To once again transmit TTY information, user 108 has to place handset 107 back into the acoustic coupler of TTY 102 before transmits TTY information to other party 109. This type of HCO operation is awkward at best. (U.S. Pat. No. 6,668,042, which is assigned to the assignee of the present submission, describes a telephone handset design that makes HCO operation a bit less cumbersome; however, even with this handset, a separate TTY device is still required in order to perform HCO operations.)
Another problem in the prior art is that the advent of the utilization of a display of a telecommunication terminal to receive instant messages (IM) and short message signaling (SMS) messaging presents a significant challenge for individuals with impaired vision. The IM messaging capability would be performed by the telecommunication system to which the telecommunication terminal is interconnected. The telecommunication system registers the presence of the user of the telecommunication terminal to presence or IM servers when the user is active on the telecommunication terminal. This allows another person an opportunity to send an IM message to the user that will be displayed on the display of the telecommunication terminal by streaming the text of the IM message across the display. The telecommunication terminal may be either a wired or wireless terminal. Within the prior art, the only solution to this problem is to add auxiliary and expensive equipment to perform the text to speech conversion.
Clearly, within the prior art, solutions for both sets of problems rely on enhancements to the endpoint configurations, typically consisting of physical devices that ordinarily would not be present on the desktop of a non-disabled user. This is important because, under Section 255 of the Telecommunications Act of 1996, the Federal Communications Commission is obligated to consider the cost of the incremental action before it can require an accessibility accommodation to be implemented. As a result, a solution that relies on additional hardware, beyond equipment that might ordinarily be available to the typical user, is unlikely to be required by the FCC and is therefore unlikely to be provided to the people who need it.